The present invention relates to a semiconductor light emitting device. Particularly, this invention relates to a structure of an InGaAlP-included semiconductor light emitting device, such as, a surface emission-type semiconductor light emitting device, suitable for optical linking devices.
Surface emission-type semiconductor light emitting devices fabricated using InGaAlP-group materials usually have light reflecting layers, each composed of semiconductor multi-films, located above and under a light emitting layer formed on an n-type GaAs-substrate.
Light emitting diodes (LEDs), among such surface emission-type semiconductor light emitting devices, with no laser oscillation, are called resonant cavity LEDs. These resonant cavity LEDs are superior to usual LEDs with no resonant structure on monochromatic emission.
Surface emission-type semiconductor light emitting devices with laser oscillation are, for example, called a vertical cavity surface emitting laser that generates a large spot laser beam.
FIG. 1 is a sectional view showing a schematic structure of a well-known surface emission-type semiconductor light emitting device.
Stacked on an n-type GaAs-substrate 101 are an n-type GaAs-buffer layer 102, a multi-film light reflecting layer 103 made of n-type semiconductors, an n-type InGaAlP-clad layer 104, an InGaAlP-active layer 105, a p-type InGaAlP-clad layer 106, and a multi-film light reflecting layer 107 made of p-type semiconductors.
Formed on the clad layer 106 and also under the clad layer 104 are current blocking layers 108 that exhibit high resistance by selective oxidation.
A current flow between a front surface electrode 110 and an rear surface electrode 111 is confined onto an opening formed on the current blocking layers 108 for light emission. The emitted light is extracted through an opening formed on the front surface electrode 110.
FIG. 2 is a sectional view showing a schematic structure of another well-known surface emission-type semiconductor light emitting device.
Elements in this device that are the same as or analogous to elements in the former device (FIG. 1) are referenced by the same reference numbers and will not be explained in detail.
The device shown in FIG. 2 is provided with current blocking layers 109 that exhibit high resistance by proton ion implantation instead of selective oxidation.
The well-known surface emission-type semiconductor light emitting devices shown in FIGS. 1 and 2 have the following disadvantages:
The first disadvantage is caused by the multi-film light reflecting layer 107 made of p-type semiconductors formed over the active layer 105.
In the devices shown in FIGS. 1 and 2, a current flows through the light reflecting layer 107 formed over the active layer 105 in the vertical direction and lately confined by the current blocking layer 108. Electrical resistance of the light reflecting layer 107 is high in both vertical and horizontal directions.
Thus, these well-known devices have high series resistance and require a high operating voltage. Moreover, these devices exhibit insufficient temperature dependence characteristics depend on heat generation due to high resistance.
The second disadvantage is an extremely small margin of positioning of the openings of the current blocking layer 108 and the front surface electrode 110.
FIGS. 3A to 5B illustrate current flow and current distribution for the well-known surface emission-type semiconductor light emitting device.
As shown in FIG. 3A, when an opening diameter d2 of the current blocking layer 108 is extremely smaller than an opening diameter d1 of the front surface electrode 110 (d1 greater than  greater than d2), a current injected from the electrode 110 flows through the p-type light reflecting layer 107 in the lateral direction and hardly reaches the center portion of the opening of the current blocking layer 108.
As illustrated in FIG. 3B, the current mostly flows in the vicinity of the opening (d2) wall, thus exhibiting un-uniform emission distribution that deviates in the vicinity of the opening wall.
On the contrary, as shown in FIG. 4A, when an opening diameter d1 of the front surface electrode 110 is smaller than an opening diameter d2 of the current blocking layer 108 (d1 less than  less than d2), a current component that flows vertically from the front surface electrode 110 (the shortest passage) drastically increases.
As illustrated by a dot line in FIG. 4B, un-uniform emission distribution is exhibited that deviates in the vicinity of the opening wall. This emission is however blocked by the front surface electrode 110 and thus cannot be extracted. This results in un-uniform emission strength observed outside, as illustrated by a solid line.
Contrary to these devices, FIGS. 5A and 5B illustrate improvement in emission strength distribution. In detail, when an opening diameter d1 of the front surface electrode 110 is little bit larger than an opening diameter d2 of the current blocking layer 108 (d1 greater than d2), a current injected from the surface electrode is diffused in a some extent in the vicinity of the center and the emission is extracted without being blocked by the front surface electrode 110.
In order to extract such uniform emission, however, the current blocking layer 108 and the front surface electrode 110 require precise fabrication so that an opening diameter d1 of the front surface electrode 110 is little bit larger than an opening diameter d2 of the current blocking layer 108 at a predetermined size.
It is difficult to control the selective oxidation in forming the current blocking layer 108 shown in FIG. 1. Thus, such a structure as shown in FIG. 5A is not always realized.
The other structure shown in FIG. 2 can be realized with precise dimension control by means of proton ion implantation for forming the current blocking layer 108. It is, however, difficult to form ohmic contact on the blocking layer 108. In detail, proton ion implantated on the light emitting surface side often causes deterioration of the semiconductor layer on the blocking layer 108. However, an arrangement such that the opening d1 of the front surface electrode 110 is made smaller than the opening d2 of the current blocking layer 10, to solve the problem, poses the problems discussed with reference to FIGS. 4A and 4B.
In order to solve the problems discussed above, a purpose of the present invention is to provide a surface emission-type semiconductor light emitting device that picks up uniform emission at high efficiency.
The present invention provides a semiconductor light emitting device including: a substrate made of a semiconductor of a first conductivity-type; a first light reflecting layer made of a semiconductor of the first conductivity-type and provided on a main surface of the substrate; an active layer made of a semiconductor including InGaAlP and provided on the first reflecting layer; a second light reflecting layer made of a semiconductor of a second conductivity-type and provided on the active layer; a current blocking layer having an opening, only through the opening a current flowing into the active layer; a transparent electrode provided on the second light reflecting layer; a front surface electrode provided on the transparent electrode and having an opening through which emission from the active layer is extracted; and a rear surface electrode provided on a rear surface of the substrate, wherein the current supplied by the transparent electrode located under the opening of the front surface electrode and flowing into the active layer through the opening of the current blocking layer causes the active layer to emit light, the light being reflected repeatedly between the first and the second light reflecting layers and extracted via the transparent electrode under the opening of the front surface electrode.
Moreover, the present invention provides a semiconductor light emitting device including: a substrate made of a semiconductor of a first conductivity-type; a first light reflecting layer made of a semiconductor of the first conductivity-type and provided on a main surface of the substrate; an active layer made of a semiconductor including InGaAlP and provided on the first light reflecting layer; a current blocking layer provided on the active layer and having an opening, only through the opening a current flowing into the active layer; a transparent electrode provided on the current blocking layer and over the active layer provided under the opening of the current blocking layer; a front surface electrode provided on the transparent electrode and having an opening through which emission from the active layer is picked up; a second light reflecting layer provided over the transparent electrode located under the opening of the front surface electrode; and a rear surface electrode provided on a rear surface of the substrate, wherein the current supplied by the transparent electrode located under the opening of the front surface electrode and flowing into the active layer through the opening of the current blocking layer causes the active layer to emit light, the light being extracted via the transparent electrode located under the opening of the front surface electrode and the second light reflecting layer.
Furthermore, the present invention provides a semiconductor light emitting device including: a substrate; a first light reflecting layer made of a semiconductor of a first conductivity-type and provided on a main surface of the substrate; a semiconductor layer made of a semiconductor of the first conductivity-type and provided on the first light reflecting layer; an active layer made of a semiconductor including InGaAlP and provided on a first portion of the semiconductor layer of the first conductivity-type; a current blocking layer provided on the active layer and having an opening, only through the opening a current flowing into the active layer; a transparent electrode provided on the current blocking layer and over the active layer provided under the opening of the current blocking layer; a first surface electrode provided on the transparent electrode and having an opening through which emission from the active layer is extracted; a second light reflecting layer provided over the transparent electrode located under the opening of the first surface electrode; and a second surface electrode provided on a second portion different from the first portion of the semiconductor layer of the first conductivity-type, wherein the current injected from the transparent electrode located under the opening of the front surface electrode and flowing into the active layer through the opening of the current blocking layer causes the active layer to emit light, the light being reflected repeatedly between the first and the second light reflecting layers.
In this invention, a semiconductor including InGaAlP represents any compound semiconductors in the III-V family expressed by the composition formula InxGayAlxP (0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61 and x+y+z=1) that include p- or n-type dopant.